1. Field of the Invention
The present invention relates to image equipment having image forming elements such as an image sensor element or a display element, and also to a vibrating device designed to vibrate the dust-screening member that is arranged at the front of each image forming element of such an image equipment.
2. Description of the Related Art
As image equipment having image forming elements, there is known an image acquisition apparatus that has an image sensor element configured to produce a video signal corresponding to the light applied to its photoelectric conversion surface. Also known is an image projector that has a display element, such as liquid crystal element, which displays an image on a screen. In recent years, image equipment having such image forming elements have been remarkably improved in terms of image quality. If dust adheres to the surface of the image forming element such as the image sensor element or display element or to the surface of the transparent member (optical element) that is positioned in front of the image forming element, the image produced will have shadows of the dust particles. This makes a great problem.
For example, digital cameras of called “lens-exchangeable type” have been put to practical use, each comprising a camera body and a photographic optical system removably attached to the camera body. The lens-exchangeable digital camera is so designed that the user can use various kinds of photographic optical systems, by removing the photographic optical system from the camera body and then attaching any other desirable photographic optical system to the camera body. When the photographic optical system is removed from the camera body, the dust floating in the environment of the camera flows into the camera body, possibly adhering to the surface of the image sensor element or to the surface of the transparent member (optical element), such as a lens, cover glass or the like, that is positioned in front of the image sensor element. The camera body contains various mechanisms, such as a shutter and a diaphragm mechanism. As these mechanisms operate, they produce dust, which may adhere to the surface of the image sensor element as well.
Projectors have been put to practical use, too, each configured to enlarge an image displayed by a display element (e.g., CRT or liquid crystal element) and project the image onto a screen so that the enlarged image may be viewed. In such a projector, too, dust may adhere to the surface of the display element or to the surface of the transparent member (optical element), such as a lens, cover glass or the like, that is positioned in front of the display element, and enlarged shadows of the dust particles may inevitably be projected to the screen.
Various types of mechanisms that remove dust from the surface of the image forming element or the transparent member (optical element) that is positioned in front of the image sensor element, provided in such image equipment have been developed.
In an electronic image acquisition apparatus disclosed in, for example, U.S. 2004/0169761 A1, a ring-shaped piezoelectric element (vibrating member) is secured to the circumferential edge of a glass plat shaped like a disc (dust-screening member). When a voltage of a prescribed frequency is applied to the piezoelectric element, the glass plat shaped like a disc undergoes a standing-wave, bending vibration having nodes at the concentric circles around the center of the glass plat shaped like a disc. This vibration removes the dust from the glass disc. The vibration (vibrational mode 1) produced by the voltage of the prescribed frequency is a standing wave having nodes at the concentric circles around the center of the disc. The dust particles at these nodes cannot be removed, because the amplitude of vibration at the nodes is small. In view of this, the glass plat shaped like a disc is vibrated at a different frequency, achieving a standing-wave vibration (vibrational mode 2) that has nodes at concentric circles different from those at which the nodes of vibrational mode 1 are located. Thus, those parts of the glass disc, where the nodes lie in vibrational mode 1, are vibrated at large amplitude. The dust-screening member is held by dust-screening member holding members that contact the dust-screening member at the nodes of standing waves that form concentric circles. The dust-screening member holding members maintain dust screening condition between the dust-screening member and the image sensor element.
Jpn. Pat. Appln. KOKAI Publication No. 2007-267189 discloses a rectangular dust-screening member and piezoelectric elements secured to the opposite sides of the dust-screening member, respectively. The piezoelectric elements produce vibration at a predetermined frequency, resonating the dust-screening member. Vibration is thereby achieved in such mode that nodes extend parallel to the sides of the dust-screening member. In order to remove dust from the nodes of vibration, the dust-screening member is resonated at different frequencies, accomplishing a plurality of standing-wave vibrational modes, thereby changing the positions of nodes. Any one of the vibrational modes achieves bending vibration having nodes extending parallel to the sides of the dust-screening member.